1,721,024 research outputs found
Lattice structures representation in 2D drawings: a proposal for a standard
No full textThe interest in the Additive Manufacturing (AM) technology is surging due to its capability of printing components with complex optimized shapes that fit industrial engineering necessities better than traditionally manufactured parts. However, conventional Computer Aided Design (CAD) software packages are often limited to deal with such complex parts, especially when the AM part is designed using lattice structures: these are structures composed of repeated small elements, called cells, across a domain which generate a light and stiff component. The scope of this work is to analyze the problem of the lattice bidimensional representation and propose a standard for representation in assembly and 2D drawings. Rules useful to handle such hierarchic structures in CAD tools is developed, and a code in Python for the open-source software FreeCadTM has been developed to evaluate the effectiveness and usability of the standard. Simplified symbols to describe complex lattice structures instead of drawing all the small elements forming the lattice have been developed. The standard is useful in technical drawings for assembly representation where lattice components are used (assembly operators, maintenance, parts catalogues). A case study is included to describe how the proposed standard could be integrated in a 2D drawing following technical product documentation production typical workflow
Additive manufacturing in automotive: advantages and criticalities
No full textAdditive Manufacturing (AM) is becoming an important alternative to traditional manufacturing
processes based on chip removal. In AM “the design drives the shape” concept is valid,
opposed to the strategy “manufacturing drives the shape” which applies with traditional parts
obtained through casting, milling, lathing processing where several design constraints should
be respected. In many industries, aerospace and automotive, the lightweight design plays an
important role on the means of transport performances. Owing to AM potentialities, a widerange
of researches are focused on methodologies to obtain structurally optimized shapes:
structures obtained through topology optimization algorithms can be manufactured only in AM
due to their complex shape. The scope of this work is to analyze advantages and criticalities
of AM in automotive applications: a case study to evaluate pros & cons of AM is included,
together with a fuel reduction analysis which can be obtained thanks to proper lightweight
design of automotive components
Numerical investigation on optimum trim envelope curve for high performance sailing yacht hulls
No full textA numerical investigation is conducted in order to identify optimum trimming attitudes for resistance reduction
in the application of high performance sailing yacht hulls. A lumped parameters model based on general unsteady
equations of motion is developed and implemented in combination with a numerical scheme to conduct
parametric studies and predict the overall performances of a specific sailing hull. Existing semi-empirical formulas
for hydrodynamic coefficients are modified and applied in order to extend the speed range of application
and obtain good agreement with available experimental data. Brief discussion of the numerical results is presented
with emphasis on the possible applications in the field of modern sailing yachts
Real-time 3D features reconstruction through monocular vision
No full textA fast and interactive implementation for camera pose registration and 3D point reconstruction over a physical surface is described in this paper. The method (called SRE—Smart Reverse Engineering) extracts from a continuous image streaming, provided by a single camera moving around a real object, a point cloud and the camera’s spatial trajectory. The whole per frame procedure follows three steps: camera calibration, camera registration, bundle adjustment and 3D point calculation. Camera calibration task was performed using a traditionalapproach based on 2-D structured pattern, while the Optical Flow approach and the Lucas-Kanade algorithm was adopted for feature detection and tracking. Camera registration problem was then solved thanks to the Essential Matrix definition. Finally a fast Bundle Adjustment was performed through the Levenberg-Marquardt algorithm to achieve the best trade-off between 3D structure and camera variations. Exploiting a PC and a commercial webcam, an experimental validation was done in order to verify precision in 3D data reconstruction and speed. Practical tests helped also to tune up several optimization parameters used to improve efficiency of most CPU time consuming algorithms, like Optical Flow and Bundle Adjustment.The method showed robust results in 3D reconstruction andvery good performance in real-time applications
3D-printing of porous structures for reproduction of a femoral bone
Full text linkBackground: 3D-printing has shown potential in several medical advances because of its ability to create patient-specific surgical models and instruments. In fact, this technology makes it possible to acquire and study physical models that accurately reproduce patient-specific anatomy. The challenge is to apply 3D-printing to reproduce the porous structure of a bone tissue, consisting of compact bone, spongy bone and bone marrow.
Methods: An interesting approach is presented here for reproducing the structure of a bone tissue of a femur by 3D-printing porous structure. Through the process of CT segmentation, the distribution of bone density was analysed. In 3D-printing, the bone density was compared with the density of infill.
Results: The zone of compact bone, the zone of spongy bone and the zone of bone marrow can be recognized in the 3D printed model by a porous density additive manufacturing method.
Conclusions: The application of 3D-printing to reproduce a porous structure, such as that of a bone, makes it possible to obtain physical anatomical models that likely represent the internal structure of a bone tissue. This process is low cost and easily reproduced
NURBS-enhanced finite element method (NEFEM) on quadrilateral meshes
Full text linkThis paper formulates quadrilateral elements for the NURBS-enhanced finite element method (NEFEM). The objective is to extend the application of NEFEM to problems where the use of quadrilateral elements is preferred. By leveraging a mapping, between reference and physical spaces, that encapsulates the exact boundary representation of the domain, a tight integration with computer aided design (CAD) systems is achieved. The contribution of this work is an enhanced quadrilateral finite element that incorporates the exact CAD geometry purely from the boundary representation (B-rep) from CAD and without the need for a whole volume representation (V-rep) as a NURBS entity. Numerical examples involving heat transfer and linear elastic problems are used to numerically demonstrate the optimal convergence properties of the method under mesh refinement
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
- …
